Linerless labels, such as shown in U.S. Pat. Nos. 3,051,588, 3,285,771, and 4,851,383, and in Canadian patent 1,248,412, are known to have advantages over conventional pressure sensitive labels which are mounted on a liner which has been coated with a release coating. In the conventional labels the liner acts as a support for transport, printing and storage, and after the label is removed from the liner it must be disposed of. A linerless label, on the other hand has the face coated with a release coating, and the back with a pressure sensitive adhesive (PSA), and is wound in a roll configuration so that the PSA is in contact with the release coating, and the release coating faces outwardly. The linerless construction offers advantages and lower costs due to substantial material reduction, elimination of disposal concerns and costs associated with release coated liners, and in providing approximately twice as many labels per roll.
While linerless labels have numerous advantages, they have not had widespread commercial acceptance, perhaps due in part to impediments to easy and clean peeling off of the PSA from the release coating in the roll format. If the adhesion of the PSA to the substrate is not strong enough (and this adhesion can degrade over time under some environmental conditions and materials), adhesive may stick to the release coating, or the substrate may be torn.
Further, there are some situations in which a roll of linerless labels is not desired. Normally, a customer needs a label dispensing machine to effectively remove labels from a roll, and the roll is either perforated at each label for separation, or a sharp peel label cutoff mechanism is necessary. In order to avoid these difficulties, according to the present invention linerless labels are provided in cut sheet format, all of the edges of the label being clean cut. Thus, a dispensing apparatus is not necessary and the product can be used with automatic applicators, storage and shipping costs are reduced, and the user of the labels can distribute various quantities to each manufacturing site.
When the linerless labels are in cut sheet form, it is important they be constructed so that robotic arms, or other automatic equipment, can easily peel one label from another. That is, minimal peel resistance must be provided, only enough to hold the labels in a stack; that is, the release coat and pressure sensitive adhesive associated with the label must be such that the force required to separate them is 0.001-1.2 ounces per inch when utilizing a standard test. Also, various different types of label, with particular coatings, can be provided utilizing this aspect of the invention.
According to the present invention, a stack of cut sheet linerless labels is provided comprising the following elements: A plurality of linerless labels, each label comprising a substrate having first and second faces, a pressure sensitive adhesive substantially completely covering the first face, and a release coat substantially completely covering the second face. The pressure sensitive adhesive and release coat having an adhesive force between them of 0.001-1.2 oz/inch (e.g. about 0.4 oz/inch), when peeling a one inch by six inch sample at a rate of twelve inches per minute at a ninety degree angle, while being sufficiently tacky to hold the labels together in a stack. The labels are disposed in a stack with the pressure sensitive adhesive of each label engaging the release coat of the next label below it.
One way to achieve the minimal adhesive force that is desired according to the invention is to provide a silicone release coat and repositional adhesive as the pressure sensitive adhesive. Typical repositional adhesives that may be utilized are Cleantac.RTM. adhesives sold by Moore Business Forms, Inc., of Lake Forest, Ill., or repositional adhesive provided on NOTESTIX.RTM. pads and business forms sold by Moore, or provided on the Post It.RTM. product sold by 3M. Alternatively permanent pressure sensitive adhesives, UV curable adhesives, and hot melt adhesives may be utilized as long as, in combination with a release coating, they meet the peel force limitation of 0.001-1.2 oz/inch.
A tie coat may be provided to enhance adherence of the pressure sensitive adhesive to the substrate, the tie coat adhering to both the substrate first face and the pressure sensitive adhesive. Alternatively, or in addition, a thermosensitive layer may be provided on the substrate second face beneath the release coat, such as shown in copending application Ser. No. 07/914,116, filed Jul. 15, 1992 (atty. ref. 263-778, 92-20) now U.S. Pat. No. 5,292,713. The labels may be constructed so that they are mailing label size (e.g., about 3 inches.times.5 inches), and printed indicia may be provided on the substrate second face beneath the release coat or on top of it. Also, a non-adhesive tab--to facilitate removal--may be provided.
The invention also contemplates a method of making a stack of cut sheet linerless labels utilizing a coating machine, and a substrate having first and second faces. The method comprises the following steps: (a) Continuously moving the substrate in a first direction through the coating machine; and substantially sequentially. (b With the coating machine, applying in a predetermined sequence to the moving substrate a pressure sensitive adhesive to the substrate first face, and a release coating to the substrate second face. (c) Cutting the substrate to form individual cut sheet labels, disconnected from previous and following labels. And (d) stacking the individual cut sheet labels into a stack with the pressure sensitive adhesive of each label engaging the release coat of an underlying label.
Step (b) may be practiced to apply the release and pressure sensitive coats (e.g., silicone release coat and repositional adhesive) so that the force required to separate them is 0.001-1.2 oz/inch (e.g. about 0.4 ounces per inch) when peeling a 1 inch.times.6 inch sample at a rate of 12 inches per minute at a 90.degree. degree angle (a standard test). Step (b) may also be practiced to apply a tie coat to the substrate first face, the pressure sensitive adhesive being applied to the tie coat; and to apply a thermosensitive layer to the substrate second face, the release coat being applied to the thermosensitive layer.
It is the primary object of the present invention to provide an advantageous linerless label stock, and a simple yet effective method for making the stock. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.